Slide valves generally are used for three general types of services including the throttling of flue gas containing solid particles, and the throttling and/or blocking of solids flow. This type of valve is used extensively in fluid catalytic cracking units (FCCU.sub.s), fluid coking units (FCU's), fluidized iron ore units (FIOR's) and other fluidized solids units where service conditions may vary between ambient and 1600.degree. F. over long periods of time and as high as 1800.degree. F. for a short time and pressures range from 0 to 250 psig. In these processes, the operating pressure is controlled by throttling the flow. Of course slide valves also have utility in various other processes. Presently, three basic types of valves are used in the type of environment discussed above, including different configurations for vertical and horizontal conduits to account for the orientation of the valve. A conventional slide valve configuration with the disc(s) in a tongue and groove guide arrangement is disclosed in U.S. Pat. No. 3,726,306. Another prior art disclosure of a tongue and groove construction is illustrated in U.S. Pat. No. 3,964,507.
In the case of fluid solids flow, both blocking and throttling valves are used. Generally, however, blocking of solids flow is accomplished by employing a single disc-type valve which covers an opening provided in a fixed orifice plate. The valve usually offers no restriction to flow when it is fully opened, i.e., the orifice opening is equal to the line diameter. Conventional throttling slide valves operate with a reduced port or opening in order to achieve the desired flow control. The orifice generally is considerably less than the line diameter depending upon the pressure drop required for proper operation. Because the valves are subject to substantially constant (solids) particle flow impingement at elevated temperatures which are high enough to significantly reduce the physical strength and hardness of the valve material, erosion of these valves is likely to occur. Erosion can substantially reduce the operating life of this key piece of equipment, which can present a major problem since the valves are a critical component of process units whose economic success is dependent on long-term uninterrupted operation. Typical prior art valves which have been employed are disclosed in U.S. Pat. Nos. 2,217,834; 2,614,789; 2,636,712; and 3,370,610.
Of these prior art patents, Lubbock, U.S. Pat. No. 2,636,712, which is assigned to the assignee of the present invention, appears most pertinent in that it discloses a slide valve/internals configuration for the flow control of solids. However, the primary emphasis of Lubbock is to compensate for erosion of valve internals by repositioning the discs relative to the seat. One or a plurality of ports (seats) can be provided in the valve orifice plates. The slides are spaced apart a desired distance to provide the desired orifice flow area. As the slides and/or orifice plates erode in the area of flow, the slide discs are moved (with the distance between maintained) relative to the openings in the orifice plate so that the eroded areas of the valve internals are removed from the flow exposure and different nonworn portions of the valve are exposed to the erosive action of the flow. Neither Lubbock or the other prior art valves have the specific construction details of the present invention or provide for a variable flow area or other advantages afforded thereby.